af_unix: Remove U_LOCK_DIAG.

sk_diag_dump_icons() acquires embryo's lock by unix_state_lock_nested()
to fetch its peer.

The embryo's ->peer is set to NULL only when its parent listener is
close()d.  Then, unix_release_sock() is called for each embryo after
unlinking skb by skb_dequeue().

In sk_diag_dump_icons(), we hold the parent's recvq lock, so we need
not acquire unix_state_lock_nested(), and peer is always non-NULL.

Let's remove unnecessary unix_state_lock_nested() and non-NULL test
for peer.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/af_unix.h

@@ -98,7 +98,6 @@ struct unix_sock {
 #define unix_state_unlock(s)	spin_unlock(&unix_sk(s)->lock)
 enum unix_socket_lock_class {
 	U_LOCK_NORMAL,
-	U_LOCK_DIAG, /* used while dumping icons, see sk_diag_dump_icons(). */
 	U_LOCK_GC_LISTENER, /* used for listening socket while determining gc
 			     * candidates to close a small race window.
 			     */

net/unix/diag.c

@@ -73,20 +73,9 @@ static int sk_diag_dump_icons(struct sock *sk, struct sk_buff *nlskb)
 
 		buf = nla_data(attr);
 		i = 0;
-		skb_queue_walk(&sk->sk_receive_queue, skb) {
-			struct sock *req, *peer;
-
-			req = skb->sk;
-			/*
-			 * The state lock is outer for the same sk's
-			 * queue lock. With the other's queue locked it's
-			 * OK to lock the state.
-			 */
-			unix_state_lock_nested(req, U_LOCK_DIAG);
-			peer = unix_sk(req)->peer;
-			buf[i++] = (peer ? sock_i_ino(peer) : 0);
-			unix_state_unlock(req);
-		}
+		skb_queue_walk(&sk->sk_receive_queue, skb)
+			buf[i++] = sock_i_ino(unix_peer(skb->sk));
+
 		spin_unlock(&sk->sk_receive_queue.lock);
 	}